(1) Field of the Invention
The present invention relates to dies for extruding honeycomb structures and a method for producing the same. More particularly, the invention relates to dies for forming honeycomb structural bodies through extruding a plastic material such as a ceramic material, wherein wear resistive alloy plates (for instance, a super hard alloy plates) are bonded, through a liquid phase diffusion welding technique, to a die base body provided with a plurality of opening holes through which the plastic material is press fed, and forming channels are provided in the wear resistive alloy plate to communicate with the opening holes. The invention also relates to a process for manufacturing such dies.
(2) Related Art Statement
As pointed out by the prior art in U.S. Pat. No. 3,790,654, there has been known a honeycomb structure forming die as shown in FIG. 1 [FIG.1(A) is a plan view of the honeycomb structure forming die, and FIG. 1(B) is a sectional side view of the die shown in FIG. 1(A) as viewed from an arrow (IB--IB)]. More particularly, the honeycomb structure forming die shown in FIGS. 1(A) and (B) is of a so-called integral structure, and is provided with honeycomb structure forming channels 3 (hereinafter referred to briefly as "forming channels") extending from a front face 1 of the die toward a rear face 2 thereof in a specified depth and in a sectional shape conforming to that of honeycomb structural bodies to be formed (in the example shown in FIG. 1, a square shape). The die is also provided with a plurality of opening holes 4 which are independently bored from the die rear face 2 toward the die front face 1 and communicate with the forming channels 3. A raw material of the honeycomb structural bodies to be formed, for instance, a ceramic plastic material is press fed to all the above plural opening holes 4, and the press fed plastic material flows into the forming channels 3 while being squeezed. Then, the plastic material is continuously extruded into ceramic honeycomb structural bodies through the forming channels 3.
However, when honeycomb structural bodies are extruded by using such a conventional honeycomb structural die, the forming channels 3 are worn with the plastic material passing through the forming channels 3, this resulting in an increase in the width of the channels. Thus, this poses a problem that expensive dies must be repeatedly exchanged so as to always assure a dimensional precision of the honeycomb structural bodies. In particular, when honeycomb structural bodies are to be formed through extrusion by using an alumina base material, a silicon carbide base material, a mullite base material, etc. having high hardness, the forming channels 3 are extensively worn. Therefore, there is an undesirable problem that the life of the die becomes conspicuously shorter.
Under the circumstances, in order to solve the above-mentioned undesirable problems, the U.S. prior art Pat. No. 4,653,996 discloses dies for extruding honeycomb structural body as shown in FIG. 2 in which a super hard alloy plate 5 is bonded to a front face of the die 1 and forming channels 3 are formed in the super hard alloy plate 5. In order to strengthen a bonded state between the super hard alloy plate 5 and the die base body 6, a well known liquid phase diffusion welding is used as a technique for bonding the super hard alloy plate 5 and the die base body 6. However, since the above liquid phase diffusion welding is carried out at high temperatures (for instance, at 1,000.degree. C.), coefficients of thermal expansion of the super hard alloy plate 5 and the die base body 6 become a problem when the liquid phase diffusion welding is employed for the bonding. That is, when there exists a large difference in the coefficient of thermal expansion between them, the super hard alloy plate is warped or voids are formed in the bonding member 7 when the bonded super hard alloy plate and die base body are cooled to room temperature after the bonding. Consequently, after the forming channels 3 are formed in a slit manner, the slit super hard alloy plate 5 is likely to peel. For this reason, the die base plate 6 is made of an alloy steel such as Invar having a coefficient of thermal expansion substantially equal to that of the above super hard alloy plate 5. Thus, this poses a problem that the manufacturing cost becomes higher.